Generally, a compressor is a device that compresses refrigerant using a rotating force of an internal motor, and is used in a refrigerator, air conditioner, etc.
Especially, as shown in FIG. 1, a motor for a compressor applied in a refrigerator is composed of a stator and a rotor, and can perform only a normal operation (for example, rotation of 3600 rpm) though there is a difference according to the characteristic of the product.
Meanwhile, the representative operation mode of the refrigerator is classified into a quick operation mode and a standard operation mode. Actually, the time when the refrigerator operates in the quick operation mode is less than 10% of the real use time of the refrigerator, and during other time, the refrigerator operates in the standard operation mode.
Conventionally, in the standard operation mode, the temperature width to be adjusted is not so large. However, in the quick operation mode, the temperature width to be adjusted is large, and thus a quick cooling is performed by driving the motor at a fixed speed, i.e., at a high speed. This high-speed operation exerts a bad effect on the refrigerator such as generation of noise, increase of power consumption, strain on the product, etc.
Nevertheless, the compressor motor of the refrigerator, irrespective of the operation mode, operates at a high speed to match the quick cooling mode.
As shown in FIG. 2, the conventional compressor motor is driven at a single speed. That is, in case of the quick operation mode, the duty rate of the motor is set as ‘1’, and the compressor motor is continuously driven irrespective of the temperature condition of the refrigerator.
In case of the standard operation mode, the compressor motor is driven to repeat an on/off operation according to a proper duty rate so that the refrigerator maintains its set temperature according to the temperature condition of the refrigerator. At this time, the load of the motor in the quick operation mode is greater than that in the standard operation mode.
As described above, since the conventional motor for the compressor is driven at the high speed irrespective of the operation mode, it has a large power consumption, and generates much noise during operation. Also, the product may be damaged due to the frequent on/off operation of the motor, and this causes the life span of the product to be shortened.